This invention relates to a copying system, and more particularly to a copying method and apparatus to copy material on opposite sides of a document on opposite sides of a sheet of material.
Copy systems for business and print shop reproduction of documents, including multi-page documents, are well known. Typically, these include an automatic document feeder, an electrostatic master imager and converter, a lithographic duplicator, and a collator. When equipped in this manner, no operator involvement is needed from the insertion of the original multi-page document to the removal of the reproduced assemblies of duplicated documents from the collator.
This type of equipment could also be used for reproducing double-sided documents. To this end, the collator is initially used in a "collect" mode, i.e. with each pocket collecting all duplicated copies from one original/master. After all the first sides (typically all odd-numbered pages) of a document are duplicated in this manner, the operator then re-inserts the original document, turned over in the document feeder, collects the duplicated copies from the collator and re-inserts them into the copy paper feeder. For the second, final run of the system, the second sides (typically all the even-numbered pages) of a document are duplicated on the blank sides of the sheets. During the second run, the collator is advantageously used in the "collate" mode. This method of operation serves the purpose of reproducing double-sided documents but requires operator actions between the first and second runs, and demands skill and attention to assure that the orientation and sequence of the pages is correct.
Systems are also known for two-side printing of documents prior to collation. In one type of system, each set of one-side printed sheets is collected in the printing machine and after the second side of the original document is exposed, this set of sheets is passed through the machine a second time for printing on the second side, after which they are forwarded to the collator. In a second type of system, two-side printing takes place in one pass of each sheet through the machine and it can be collated immediately. The first of these types of systems has been used on xerographic copying machines, and as such requires manual positioning of the original document just prior to each passage of the copy sheets through the machine. Compatible automatic document feeding is not known for this type of system. The second type of system requires significantly greater machine investment and is not readily adaptable to automatic feeding of the original document.